Machine tool tracer

ABSTRACT

A contour milling machine having profile and depth tracers with tracing styli adapted to be displaced by workpiece templates for controlling the relative position of a machine cutter and a workpiece. A photoelectric signaling device of each tracer comprising a stationary mask and a movable mask operable by the respective tracing stylus is operable to generate an electric signal for controlling the relative position of the workpiece and cutter in accordance with the displacement of the tracing stylus.

United States Patent 1191 Campbell I Sept. 4, 1973 1 MACHINE TOOL TRACER2,410,093 10/1946 Martinec 33/172 E Inventor: Paul J Campbell The New2,086,153 7/1937 yBlckel 90/62 A England Machine and Tool Company 75 3 pRod Rd Primary Examiner-Andrew R. Juhasz Moodus, Conn 0 037 AssistantExaminer-Z. R. Bilinsky I Att0rneyPrutzman, Hayes, Kalb & Chilton [22]Filed: June 4, 1971 [21] Appl. No.: 150,063 [57] ABSTRACT A contourmilling machine having profile and depth [52] CL 90/62 33/23 022 tracerswith tracing styli adapted to be displaced by Int Cl q 35/26 workpiecetemplates for controlling the relative posi- [58] Field of Search 90/62A; 82/14 B; "9" l and a workpece' Pl 250/231 R 33/172 E 23 K tric signamg device of each tracer comprising a stationary mask and a movable maskoperable by the re- References Cited spect ve tracing stylus s operableto generate an electr1c signal for controlling the relative position ofthe UNITED STATES PATENTS workpiece and cutter in accordance with thedisplace- 3,229,587 1/1966 Chauvel 90/62 A ment of the tracing stylus.,557,379 1/1971 Kelsey 250/23] R n HHMHW 2,704,956 3/1955 Johnson 90/62A 19 Claims, 11] Drawing Figures Patented Sept. 4, 1973 3 Sheets-Sheet 1W F IG. 2 07 a Y AXIS 7 M] /Z PHOTOELECTRIC STABILIZING CONTROL CIRCUITNETWORK x AXIS PHOTOELECTRIC STABILIZING g; CONTROL CIRCUIT NETWORK lfiQ w W BYW INVENTOR ATTORNEYS Patented Sept. 4, 1973 3,756,122

5 Sheets-Sheet 3 Patented Sept. 4, 1973 3,756,122

3 Sheets-Sheet 5 MACHINE TOOL TRACER BRIEF SUMMARY OF THE INVENTION Thepresent invention relates generally to machine tool tracers of the typehaving a tracing stylus cooperable with a suitable template forcontrolling the relative position of a machine tool cutter and aworkpiece for machining the workpiece in accordance with the contour ofthe template.

It is a primary aim of the present invention to provide in a machinetool tracer of the type described a new and improved signal generatingmeans operable by the tracing stylus for generating a control signal forcontrolling the relative position of a machine tool cutter and aworkpiece. It is a more specific aim of the present invention to providea new and improved photoelectric signal generating device useful in aprofile tracer for two dimensional control of the contour of a workpieceand in a depth tracer for controlling the workpiece contour along athird dimension.

It is another aim of the present invention to provide new and improvedprofile and depth tracers useful alone or in combination in a machinetool such as a milling machine for controlling the relative position ofa machine tool cutter and a workpiece.

It is a further aim of the present invention to provide a new andimproved profile tracer of the type shown and described in U. S. Pat.No. 2,704,956 of Clarence Johnson dated Mar. 29, 1955 and entitledContouring Control Mechanism which is cooperable with a suitabletemplate for accurately machining a workpiece in accordance with theprofile of the template.

It is a still further aim of the present invention to provide a new andimproved depth tracer for controlling the depth of cut of a machine toolcutter.

Other objects will be in part obvious and in part pointed out more indetail hereinafter.

A better understanding of the invention will be obtained from thefollowing detailed description and the accompanying drawings ofillustrative applications of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a front elevation view of a milling machine having profile anddepth tracers incorporating embodiments of the present invention;

FIG. 2 is a generally diagrammatic view of a profile tracer controlsystem of the milling machine;

FIG. 3 is an enlarged front elevation section view, partly broken awayand partly in section, of the profile tracer;

FIG. 4 is a transverse section view, partly broken away and partly insection, of the profile tracer taken substantially along line 4-4 ofFIG. 3;

FIG. 5 is a transverse section view, partly in section, of the profiletracer taken substantially along line 55 of FIG. 3;

FIG. 6 shows an enlargement of a portion of the section view of FIG. 5;

FIG. 7 is a transverse section view, partly in section, of the profiletracer taken substantially along line 7--7 of FIG. 3;

FIG. 8 is an enlarged front elevation view, partly broken away andpartly in section, of the depth tracer;

FIG. 9 is an enlarged partial side elevation view, partly broken awayand partly in section, of the depth tracer; and

FIG. 10 is a transverse section view, partly in section, of the depthtracer taken substantially along line l0l0 of FIG. 8.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings in detail wherein like numbers represent like parts throughoutthe several figures, an automatic contour milling machine 10 having aprofile tracer l2 and a depth tracer l4 incorporating embodiments of thepresent invention is shown comprising a single vertical spindle 16 forsupporting a suitable cutter 18 for cutting a workpiece (not shown)supported on a workpiece support 20 of a table 22. The table 22 ismounted on suitable ways (not shown) for being laterally positioned by afeed screw 26 (FIG. 2) driven by a suitable high torque, low speed,reversible DC motor 27. A cross slide 30 operated by a similar motordriven feed screw 32 (FIG. 2) provides for positioning the cutter l8fore-and-aft relative to the table 22, and a spindle slide 33 providesfor positioning the cutter l8 vertically relative to the table 22.

The profile tracer l2 and depth tracer 14 are mounted for fore-and-aftand vertical movement with the spindle slide 33 for cooperation withsuitable templates mounted on a raised template support 36 of the tablefor controlling the lateral position of the table table 22 (along an Xaxis), the fore-and-aft position of the cross slide 30 (alonga Y axis)and the vertical position of the spindle slide (along a Z axis). Moreparticularly the profile tracer I2 is operable to control the lateralposition of the table 22 and the fore-and-aft position of the crossslide 30, and the depth tracer 14 is operable for controlling thevertical position of the spindle slide 33. As is well known, the profileand depth tracers l2, 14 may be independently used or be simultaneouslyused for combined profile and depth contour control.

Referring to FIGS. 3-7, the profile tracer 12 comprises a multi-parthousing or frame 40 with a lower support 42 and an upper cover 44detachably secured to the lower support 42. A dependling tracer spindle50 is mounted on the lower support 42 for pivotal movement from itsnormal or vertical axis by a ball" 54 provided on the spindle and anannular nylon socket or seat 56 for the ball 54 mounted on the support42. The tracing spindle 50 has a detachable stylus 58 engageable with asuitable template for pivoting the spindle 50 and for therebycontrolling the relative position of the cutter 18 and workpiece alongthe X and Y axes as explained more fully hereinafter.

An intermediate support piece: 60 secured to the upper end of the lowersupport 42 has a depending colhr 62 loosely receiving the spindle 50 forpermitting limited pivotal movement thereof. An annular coil assembly 64is mounted on the lower end of the collar 62 for magnetizing the stylus58, for which purpose the spindle 50, including its stylus 58, are madeof a suitable magnetically permeable material. Also, the associatedtemplate (not shown) is made of a suitable magnetically permeablematerial to provide for magnetically attracting the stylus 58 intoengagement with the template.

For the reasons described in more detail in the aforementioned U. S.Pat. No. 2,704,956, the spindle 50 is rotated for automatically feedingthe stylus 58 along the associated template and as a result for feedingthe cutter 18 laong the workpiece (in a direction which depends on thedirection of rotation of the spindle 50). In

, the shown embodiment the spindle 50 is driven by a suitable reversiblemotor (not shown) through a pulley drive 80 (FIG. 4), worm 82, wormwheel 84, a depending plastic drive sleeve 86 (FIG. 3) and a pair ofball bearings 88 mounted on a shaft 90 extending diametrically throughthe spindle ball 54. The ball bearings 88 are received within axiallyextending diametrically opposed slots in the drive sleeve 86, and thesleeve 86 is pivotally mounted by pins 94 on a worm wheel support ring92 (for pivotal movement about an axis parallel to the axis of the shaft90) for permitting unimpaired pivotal movement of the spindle 50 whileit is rotated. The worm wheel support 92 is rotatably mounted on thecollar 62 by a ball bearing 100, and a wave spring 102 is mountedbetween the upper edge of the coil assembly 64 and the inner race of theball bearing 100 to bias a cover 104 (supported on worm wheel 84)against a roller thrust bearing 106.

A photoelectric signaling device 110 having an inverted support cup1l2'is mounted on the intennediate support piece 60 and secured to thelower support 42 therewith. Two 90 spaced pairs of diametrically opposedset screws 116 are mounted on the support cup 112 for engagement with anupstanding annular flange 118 of the support piece 60 for accuratelypositioning the signaling device 110 coaxially with the spindle 50 (withthe spindle in its normal or vertical position). Upper and lower supportrings 120, 121 of the signaling device 110 are mounted on opposite sidesof a base 122 of the inverted cup 112, and a limit switch 123 issuitably mounted on the housing cover 44 with its operating button 124substantially coaxial with the spindle 50. A pivotal triangular locatingplate 126 having outer edges received within an annulus in the ring 120and held in position (in engagement with the switch button 124) by atension spring 128 provides a seat 129 for the upper end of a controlpin 130 having an enlarged lower head with a ball bearing 134 engagingan upper conical edge of the spindle 50. The switch 123 is suitablyconnected for deactivating the milling machine and is mounted so thatthe switch is actuated to deactivate the machine when the control pin130 is raised approximately 0.02 inches. The ball 54 and its supportingseat 56 are contoured to axially raise the control pin 130 and tothereby depress the switch button 124 sufficiently to deactivate themilling machine when the spindle is pivoted some predesigned maximumlimit. Accordingly, if the stylus 58 were deflected for example 0.005inches, the switch 123 would be actuated to deactivate the machine.

A pair of substantially identical photoelectric units 139, 140, eachcomprising a radiant energy transmitting diode 141 and a photoelectricreceiver diode 142, are provided for respectively sensing tracing stylusdeflection in the lateral direction (along the X axis) and in thefore-and-aft direction (along the Y axis). The two photoelectric units139, 140 are angularly spaced 90 and positioned relative to the verticalaxis of the spindle 50 for sensing the components along the X and Y axesrespectively of the deflection of the stylus 58. The transmitter diode141 may for example be a Gallium-Arsenide Infrared Emitter Diode No.40598A sold by Radio Corporation of America and the photoelectricreceiver diode 142 may for example be a LS-400 N-P-N Planar SiliconPhoto Diode sold by Texas Instruments Inc. The transmitter diode 141 andreceiver diode 142 are mounted in axial alignment on the support rings121, respectively on an axis parallel to the vertical axis of thespindle 50, and suitable 90 spaced openings are provided on the base 122for receiving the transmitter diodes 141.

A flat annular shutter disc or masking ring 150 having an inner circulartapered edge defining a central opening 152 snugly receiving the controlpin is mounted on the cup base 122 for being laterally shifted by thecontrol pin 130. A leaf spring 153 is mounted on the disc for engagementwith the control pin 130 for preventing play between the control pin anddisc. The disc 150 is accurately machined and is provided with an outercircular tapered edge for variably masking the infrared transmitterdiodes 141 as the disc 150 is shifted by the spindle 50. Also, an outerstationary circular mask 154 is formed on the support ring 120 formasking an outer peripheral portion of the infrared transmitter diodes141. The stationary circular mask 154 covers or masks an outerapproximately one-third portion of each infrared transmitter diode 141and the inner mask 150 provides for masking an inner approximatelyone-third portion of each infrared transmitter diode 141 when thespindle 50 is vertical. Accordingly an approximately one-third centralportion of each infrared transmitter diode 141 is unmasked or exposedwith the stylus centered.

When the stylus 58 is deflected in one direction, the inner mask 150 isshifted in the opposite direction (by approximately the same amount) tovary the unmasked or active area of one or both of the infraredtransmitter diodes 141 (depending on the direction of deflection of thestylus 58). Referring to FIG. 2, each photoelectric receiver diode 142forms a part of a suitable control circuit 158 operable for generatingan output signal voltage (in a lead 159) having a magnitude proportionalto the magnitude of the deflection of the tracer stylus 58 and apolarity (plus or minus) dependent upon the direction of deflection ofthe stylus 58 from its normal or center position. The output signalvoltage from the control circuit 158 is modified with respect to time bya suitable servo-stabilizing network 160 and applied to the inputterminals of a suitable servo power amplifier 161 for operating therespective feed motor 27 in the appropriate direction (for returning thetracer spindle to its vertical or normal position) and at a speed andtorque depending on the magnitude and the rate of change of deflectionof the stylus 58. Each photosensitive diode 142 is arranged in itsrespective control circuit 158 in such a way that the output signalvoltage from the circuit 158 is zero when the radiant energy reachingthe diode 142 is at a pre-established mid range value and departssignificantly from zero in response to a very small departure in theamount of radiant energy from said mid range value. Typically, adeflection of the stylus 58 of 0.0001 inches from its normal or centerposition is sufficient to cause enough change in light intensityreaching the diode 142 to operate the feed motor 27. Thus, thephotoelectric control provides for operating each motor 27 in bothdirections without any deadband at reversal for continually moving therespective tracer stylus towards center. Also, the photoelectric controlis manually adjustable for accurately prcsetting the motor reversal atthe tracer stylus center position. For this purpose a manuallyadjustable potentiometer or regulator H63 is provided for controllingthe intensity of the infrared emitter diode 141 and for thereby settingthe intensity of the infrared radiation reaching the photosensitivediode 142 when the tracer spindle 50 is vertical, to a value that bringsthe output of circuit 160 to zero volts.

As indicated the opposed edges of the movable and stationary masks 150,154 have a lateral separation equal to approximately one-third thediameter of the infrared transmitter diode 141 when the tracer spindle50 is centered (whereupon the masks 150, 154 block a majority of theperipheral relatively low intensity radiant energy from the transmitterdiode M1) to substantially increase the percentage change in radiantenergy reaching the photoelectric receiver diode 142 for any givenlateral deflection of the stylus 58 from center. Accordingly thesensitivity and responsiveness of the tracer is substantially increasedand, it has been found, the profile tracer is sufficiently responsive toprovide for profile tracing within a 0.0001 inch accuracy.

Referring to FIGS. 8-10, the depth tracer 14 comprises a multi-parthousing or frame 200 with an intermediate annular support ring 202, anda lower support 204 and upper cover 206 detachably secured to the ring202. A depending vertical spindle 210 mounted on the housing 200comprises a pair of flat bearing walls 212, 214 extending parallel tothe axis of the spindle and at right angles to each other. Two pairs216, 218 of ball bearings 220 are mounted on shafts 222 supported onintegral stanchions 223-225 of the lower support 204 for engagement withthe spindle bearing walls 212, 214 respectively. The shafts .222 aremounted with their axes mutually perpendicular and perpendicular to thevertical or normal axis of the spindle 210 such that the spindle issupported for vertical or axial movement on the bearings 220. Thespindle 210 is held in engagement with the bearings 220 by a compressionspring 228 acting through a pin 230 having an inner rounded end engaginga tapered seat of the spindle. A screw 232 threaded into theintermediate support ring 202 is provided for mounting the pin 230 andcompression spring 228. The common axis of the compression spring 228and pin 230 lies in the plane of the bearing axes and extends at anangle of substantially 45 to each bearing axis and such that the spindle210 may be pivoted in any direction while being maintained in engagementwith both pairs of bearings 220.

A photoelectric signaling device 240 is provided for controlling thevertical position of the spindle slide 33 in the manner of the controlof the table position and cross slide position by the profile tracer 12.A support ring 242 of the signaling device 240 is secured to the upperface of the intermediate ring 202 coaxially with the vertical axis ofthe spindle 210 and a lever arm 244 is supported (by ball bearings 24Smounted on a pair of aligned pivot pins 246 extending inwardly from thesupport ring 242) for pivotal movement about an axis 248 extendingperpendicular to and laterally offset from the vertical spindle axis. Anadjustable threaded stop 250 having a lock nut 252 is mounted on thelever arm 244 above the spindle and a thrust ball bearing 254 is mountedbetween concave conical seats 256, 258 on opposed ends of the spindle210 and stop 250 to provide for pivoting the lever arm 244 with thespindle 210 (by axially shifting and/or pivoting the spindle). A mask orshutter 260 is mounted on the lever arm 244 for receipt within a radialslot 262 in the ring 242 and has a downwardly facing straight edgeengageable with an upwardly facing straight edge of a stationary mask263 formed on the ring 262. The stationary mask 263 thereby forms a stopfor limiting the pivotal motion of the lever arm 244 in the clockwisedirection as viewed in FIG. 8.

A pair of identical tension springs 266 are connected between the leverarm 244 and spindle 210 for biasing the spindle upwardly into engagementwith the lever arm stop 250 and for biasing the lever arm 244, clockwiseas viewed in FIG. 8, to pivot the mask 260 into engagement with thestationary mask 263. The axes of the tension springs 266 are parallel toand on opposite sides of and at equal distances from the axis of thespindle 210 for biasing the spindle 210 in the upward direction only.The tension springs are, however, unevenly spaced from the pivot axis248 on opposite sides thereof to provide for biasing the lever arm 244in the clockwise direction as viewed in FIG. 8.

A photoelectric unit 270, comprising an infrared transmitter diode 141and a photoelectric receiver diode 142, is mounted within aligned boresin the support ring 242 along an axis parallel to the pivotal axis 248of the lever arm 244 and with the diodes 141, 142 on opposite sides ofthe stationary mask 263. The stationary mask 263 is dimensioned to maskapproximately a one-third peripheral portion of the transmitter diode141 and the pivotal mask 260 and stationary mask 263 cooperate tocontrol the intensity of the radiant energy on the photoelectricreceiver diode 142 in the manner of the stationary and reciprocablemasks of the profile tracer 12. Also, the pivotal mask 260 coversapproximately a one-third peripheral portion of the transmitter diode141 (and is therefore spaced from the stationary mask 263 by an amountequal to approximately one-third the diameter of the transmitter diode141) when the spindle is in a neutral position. The photoelectricreceiver diode 142 forms a part of a control circuit (not shown butwhich may be substantially identical to the control circuits 158) foroperating a feed screw motor (not shown) for controlling the verticalposition of the spindle slide 33 (along the Z axis) in the manner theprofile tracer 12 controls the movement of the table and cross slide(along the X and Y axes respectively).

Referring to FIG. 8, the vertical or normal axis of the spindle 210 liesapproximately one-fifth the distance between the pivotal axis 248 of thelever arm 244 and the vertical center line of the photoelectric unit 270and therefore any vertical motion of the spindle 210 is amplified (inthe shown embodiment approximately five times) to provide a verysensitive mask control. Also, any lateral deflection of the tracingstylus 241 causes pivotal movement of the lever arm 244 which isamplified through the action of the thrust ball bearing 254 on theconical seat 256. Accordingly where the tracing stylus 241 is deflectedlaterally due for example to engagement with a steep template surface,the photoelectric unit 270 will be operated to generate a signal forsuitably raising the spindle slide 33.

As will be apparent to persons-skilled in the art, variousmodifications, adaptations and variations of the foregoing specificdisclosure can be made without departing from the teachings of thepresent invention.

I claim:

1. In a tracing system useful with a workpiece template for operatingreversible motor means of a machine tool in reverse directions thereoffor machining a workpiece in accordance with the contour of thetemplate, comprising a support, a tracing spindle mounted on the supporthaving a tracing stylus cooperable with a template for displacement inopposite directions through an established intermediate position thereofin accordance with the contour of the template and the operation of thereversible motor means, and motor control means for operating the motormeans in reverse directions thereof in accordance with the displacementof the tracing stylus in opposite directions thereof respectively fromits established intermediate position, the improvement wherein the motorcontrol means comprises a photoelectric unit having a radiant energytransmitter, a photoelectric receiver mounted in alignment with thetransmitter for receiving radiant energy therefrom, and a mask mountedintermediate the transmitter and receiver for being shifted for varyingthe intensity of radiant energy on the receiver and connected to thespindle to be shifted in opposite directions as the stylus is disposedin opposite directions respectively through its said establishedintermediate position, the shiftable mask being positioned, with thespindle in its said established intermediate position, for masking afirst significant portion of the transmitter for masking from thereceiver a first significant amount of the radiant energy from thetransmitter, and with a second significant portion of the transmitterunmasked to permit receipt on the receiver of a second base level amountof radiant energy from the transmitter, and means operable by thephotoelectric receiver for operating the reversible motor means in firstand second reverse directions thereof in accordance with the increaseand decrease level of radiant energy on the receiver relative to saidbase level of radiant energy on the receiver.

2. In a tracing system according to claim 1 wherein the motor controlmeans comprises adjustable means for establishing the intermediateposition of the tracing stylus, where the operation of the reversiblemotor means is reversed, by adjustment of the base amount of radiantenergy on the receiver.

3. In a tracing system according to claim 1 wherein said photoelectricunit comprises a stationary mask intermediate the transmitter andreceiver for masking a third peripheral portion of the transmitter andwherein the shiftable mask and stationary mask are relatively positionedand contoured so that the shiftable mask is shifted by the spindletoward and away from the stationary mask for varying the intensity ofradiant energy on the receiver.

4. In a tracing system according to claim 3 wherein the shiftable andstationary masks have opposed complementary mask edges.

5. In a tracing system according to claim 3 wherein the shiftable andstationary masks provide for masking substantially equal peripheralportions of the transmitter with the stylus in its establishedintermediate position.

6. In a tracing system according to claim 1 wherein the reversible motormeans provides at least two dimensional control of the machiningoperation, wherein the spindle is mounted for two dimensionaldisplacement of the tracing stylus, and wherein the motor control meanscomprises a pair of said photoelectric units with shiftable masksconnected to the spindle to be shifted in opposite directions inaccordance with the displacement vectors of the tracing stylus alongmutually perpendicular axes respectively, and wherein the shiftablemasks of the pair of photoelectric units are provided by a singlemasking member.

7. In a tracing system according to claim 6 wherein said single maskingmember is circular.

8. In a tracing system according to claim 6 wherein each of thephotoelectric units comprises a stationary mask intermediate thetransmitter and receiver for masking a third peripheral portion of thetransmitter and wherein the shiftable mask and stationary mask of eachphotoelectric unit are relatively positioned and contoured so that theshiftable mask is shifted by the spindle toward and away from thestationary mask for varying the intensity of radiant energy on thereceiver.

9. In a tracing system according to claim 6 wherein the spindle iselongated and the pair of photoelectric units are angularly spacedsubstantially about the longitudinal axis of the spindle with thetracing stylus in its said intermediate position.

10. In a tracing system according to claim 9 wherein the single maskingmember is circular.

11. A tracing system according to claim 9 wherein the spindle is mountedto be rotated about its longitudinal axis and further comprising meansfor rotating the spindle while permitting displacement of the tracingstylus, and means interconnecting the upper end of the spindle with themasking member for shifting the masking member in a direction dependingon the direction of displacement of the tracing stylus.

12. A machine tool tracer cooperable with a workpiece template forcontrolling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established intermediateposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established intermediateposition, and a stationary mask intermediate the transmitter andreceiver for masking a first peripheral portion of the transmitter, theshiftable mask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter for masking from the receiver a first significant amount ofradiant energy from the transmitter and with a third significant portionof the transmitter unmasked to permit receipt on the receiver of asecond significant base level amount of radiant energy, and theshiftable and stationary masks being relatively and contoured so thatthe shiftable mask is shifted by the spindle toward and away from thestationary mask for varying the intensity of radiant energy on thereceiver, and means operable by the photoelectric receiver for operatingthe reversible motor means in first and second reverse directionsthereof in accordance with the increase and decrease respectively of thelevel of radiant energy on the receiver relative to said base level ofradiant energy on the receiver.

13. A machine tool tracer according to claim 12 wherein the spindle iselongated and is mounted on said support for movement of the tracingstylus in all directions through its said established intermediateposition, wherein the tracer comprises a pair of said photoelectricunits angularly spaced substantially 90 about the longitudinal axis ofthe spindle in its established intermediate position, and wherein theshiftable masks of the pair of photoelectric units are provided by asingle masking member connected to be shifted by the spindle in a planesubstantially perpendicular to the longitudinal axis of the spindle inits said intermediate position for variably masking the radiant energytransmitters of the photoelectric units in accordance with thedisplacement vectors of the tracing stylus along mutually perpendicularaxes respectively.

14. A machine tool tracer according to claim 13 wherein the spindle ismounted for rotation about its longitudinal axis, and wherein the tracercomprises drive means for rotating the spindle about its longitudinalaxis without effecting the displacement of the tracing stylus from itsestablished intermediate position, and connector means interconnectingthe spindle and masking member for shifting the masking member inaccordance with the displacement of the tracing stylus from itsestablished intermediate position.

15. A machine tool tracer cooperable with a workpiece template forcontrolling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established intermediateposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established interrnediateposition, a stationary mask intermediate the transmitter and receiverfor masking a first peripheral portion of the transmitter, the shiftablemask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter and with a third significant portion of the transmitterunmasked, and the shiftable and stationary masks being relativelypositioned and contoured so that the shiftable mask is shifted by thespindle toward and away from the stationary mask for varying theintensity of radiant energy on the receiver, the spindle being elongatedand being mounted on said support for movement of the tracing stylus inall directions through its said established intermediate position, apair of said photoelectric units angularly spaced substantially 90 aboutthe longitudinal axis of the spindle in its established intermediateposition, and the shiftable masks of the pair of photoelectric unitsbeing provided by a single masking member connected to be shifted by thespindle in a plane substantially perpendicular to the longitudinal axisof the spindle in its said intermediate position for variably maskingthe radiant energy transmitters of the photoellectric units inaccordance with the displacement vectors of the tracing stylus alongmutually perpendicular axes respectively, the spindle being mounted forrotation about its longitudinal axis, drive means for rotating thespindle about its longitudinal axis without effecting the displacementof the tracing stylus from its established intermediate position,connector means interconnecting the spindle and masking member forshifting the masking member in accordance with the displacement of thetracing stylus from its established intermediate position, the drivemeans comprising a pivotal drive sleeve surrounding the spindle andpivotal about an axis extending transversely of the longitudinal axis ofthe spindle in its established intermediate position, the drive sleevehaving a pair of diametrically opposed slots, and a pair of guiderollers received within said slots and mounted on the spindle forrotation about an axis extending generally parallel to the pivotal axisof the drive sleeve.

16. A machine tool tracer cooperable with a workpiece template forcontrolling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established interrnedaiteposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity'ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established intermediateposition, a stationary mask intermediate the transmitter and receiverfor masking a first peripheral portion of the transmitter, the shiftablemask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter and with a third significant portion of the transmitterunmasked, and the shiftable and stationary masks being relativelypositioned and contoured so that the shiftable mask is shifted by thespindle toward and away from the stationary mask for varying theintensity of radiant energy on the receiver, the spindle being elongatedand being mounted to be displaced in opposite directions generallyparallel to its longitudinal axis, the shiftable mask being pivotallymounted and connected for being pivotally shifted by the spindle, andthe spindle being mounted for pivotal displacement as well aslongitudinal displacement and means interconnecting the pivotal mask andspindle for pivoting the mask by pivotal displacement of the spindle.

17. A machine tool tracer according to claim 16 wherein theinterconnecting means comprises a pair of opposed ball seats on the maskand at one end of the spindle and a ball bearing received in saidopposed seats.

18. A machine tool tracer cooperable with a workpiece template forcontrolling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established intermediateposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established intermediateposition, a stationary mask intermediate the transmitter and receiverfor masking a first peripheral portion of the transmitter, the shiftablemask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter and with a third significant portion of the transmitterunmasked, and the shiftable and stationary masks being relativelypositioned and contoured so that the shiftable mask is shifted by thespindle toward and away from the stationary mask for varying theintensity of radiant energy on the receiver, the spindle being elongatedand being mounted on said support for movement of the tracing stylus inall directions through its said established intermediate position, apair of said photoelectric units angularly spaced substantially 90 aboutthe longitudinal axis of the spindle in its established intermediateposition, the shiftable masks of the pair of photoelectric units beingprovided by a single masking member connected to be shifted by thespindle in a plane substantially perpendicular to the longitudinal axisof the spindle in its said intermediate position for variably maskingthe radiant energy transmitters of the photoelectric units in accordancewith the displacement vectors of the tracing stylus along mutuallyperpendicular axes respectively, a ball and socket support for thespindle for mounting the spindle for pivotal movement in all directionsfrom its established intermediate position and contoured tolongitudinally shifted the spindle upon pivotal displacement thereof,and a control switch connected to be actuated by the spindle upon apredetermined longitudinal displacement thereof 19. A machine tooltracer cooperable with a workpiece template for controlling a workpiecemachining operation comprising a support, a tracing spindle mounted onthe support for displacement in opposite directions through anestablished intermediate position thereof and having a tracing styluscooperable with a workpiece template for displacement in oppositedirections through an established intermediate position thereofcorresponding to the established intermediate position of the spindle, aphotoelectric unit having a radiant energy transmitter, a photoelectricreceiver in alignment with the transmitter for receiving radiant energytherefrom for producing a machine tool control signal, a shiftable maskmounted intermediate the radiant energy transmitter and receiver forbeing shifted for varying the intensity of radiant energy on thereceiver and connected to the spindle to be shifted in oppositedirections as the tracing stylus is displaced in opposite directionsrespectively through its established intermediate position, a stationarymask intermediate the transmitter and receiver for masking a firstperipheral portion of the transmitter, the shiftable mask beingpositioned, with the stylus in its said established intermediateposition, for masking a second significant portion of the transmitterand with a third significant portion of the transmitter unmasked, andthe shiftable and stationery masks being relatively positioned andcontoured so that the shiftable mask is shifted by the spindle towardand away from the stationary mask for varying the intensity of radiantenergy on the receiver, the spindle being elongated and being mounted tobe displaced in opposite directions generally parallel to itslongitudinal axis and the shiftable mask being pivotally mounted forpivotal movement about an axis extending substantially perpendicular toand laterally offset from the longitudinal axis of the spindle and beingconnected for being pivotally shifted by the spindle, and spring meansinterconnecting the spindle and pivotal mask for biasing the mask in onepivotal direction for increasingly masking the transmitter and biasingthe spindle in a longitudinal direction toward the mask.

1. In a tracing system useful with a workpiece template for operatingreversible motor means of a machine tool in reverse directions thereoffor machining a workpiece in accordance with the contour of thetemplate, comprising a support, a tracing spindle mounted on the supporthaving a tracing stylus cooperable with a template for displacement inopposite directions through an established intermediate position thereofin accordance with the contour of the template and the operation of thereversible motor means, and motor control means for operating the motormeans in reverse directions thereof in accordance with the displacementof the tracing stylus in opposite directions thereof respectively fromits established intermediate position, the improvement wherein the motorcontrol means comprises a photoelectric unit having a radiant energytransmitter, a photoelectric receiver mounted in alignment with thetransmitter for receiving radiant energy therefrom, and a mask mountedintermediate the transmitter and receiver for being shifted for varyingthe intensity of radiant energy on the receiver and connected to thespindle to be shifted in opposite directions as the stylus is disposedin opposite directions respectively through its said establishedintermediate position, the shiftable mask being positioned, with thespindle in its said established intermediate position, for masking afirst significant portion of the transmitter for masking from thereceiver a first significant amount of the radiant energy from thetransmitter, and with a second significant portion of the transmitterunmasked to permit receipt on the receiver of a second base level amountof radiant energy from the transmitter, and means operable by thephotoelectric receiver for operating the reversible motor means in firstand second reverse directions thereof in accordance with the increaseand decrease level of radiant energy on the receiver relative to saidbase level of radiant energy on the receiver.
 2. In a tracing systemaccording to claim 1 wherein the motor control means comprisesadjustable means for establisHing the intermediate position of thetracing stylus, where the operation of the reversible motor means isreversed, by adjustment of the base amount of radiant energy on thereceiver.
 3. In a tracing system according to claim 1 wherein saidphotoelectric unit comprises a stationary mask intermediate thetransmitter and receiver for masking a third peripheral portion of thetransmitter and wherein the shiftable mask and stationary mask arerelatively positioned and contoured so that the shiftable mask isshifted by the spindle toward and away from the stationary mask forvarying the intensity of radiant energy on the receiver.
 4. In a tracingsystem according to claim 3 wherein the shiftable and stationary maskshave opposed complementary mask edges.
 5. In a tracing system accordingto claim 3 wherein the shiftable and stationary masks provide formasking substantially equal peripheral portions of the transmitter withthe stylus in its established intermediate position.
 6. In a tracingsystem according to claim 1 wherein the reversible motor means providesat least two dimensional control of the machining operation, wherein thespindle is mounted for two dimensional displacement of the tracingstylus, and wherein the motor control means comprises a pair of saidphotoelectric units with shiftable masks connected to the spindle to beshifted in opposite directions in accordance with the displacementvectors of the tracing stylus along mutually perpendicular axesrespectively, and wherein the shiftable masks of the pair ofphotoelectric units are provided by a single masking member.
 7. In atracing system according to claim 6 wherein said single masking memberis circular.
 8. In a tracing system according to claim 6 wherein each ofthe photoelectric units comprises a stationary mask intermediate thetransmitter and receiver for masking a third peripheral portion of thetransmitter and wherein the shiftable mask and stationary mask of eachphotoelectric unit are relatively positioned and contoured so that theshiftable mask is shifted by the spindle toward and away from thestationary mask for varying the intensity of radiant energy on thereceiver.
 9. In a tracing system according to claim 6 wherein thespindle is elongated and the pair of photoelectric units are angularlyspaced substantially 90* about the longitudinal axis of the spindle withthe tracing stylus in its said intermediate position.
 10. In a tracingsystem according to claim 9 wherein the single masking member iscircular.
 11. A tracing system according to claim 9 wherein the spindleis mounted to be rotated about its longitudinal axis and furthercomprising means for rotating the spindle while permitting displacementof the tracing stylus, and means interconnecting the upper end of thespindle with the masking member for shifting the masking member in adirection depending on the direction of displacement of the tracingstylus.
 12. A machine tool tracer cooperable with a workpiece templatefor controlling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established intermediateposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established intermediateposition, and a staTionary mask intermediate the transmitter andreceiver for masking a first peripheral portion of the transmitter, theshiftable mask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter for masking from the receiver a first significant amount ofradiant energy from the transmitter and with a third significant portionof the transmitter unmasked to permit receipt on the receiver of asecond significant base level amount of radiant energy, and theshiftable and stationary masks being relatively and contoured so thatthe shiftable mask is shifted by the spindle toward and away from thestationary mask for varying the intensity of radiant energy on thereceiver, and means operable by the photoelectric receiver for operatingthe reversible motor means in first and second reverse directionsthereof in accordance with the increase and decrease respectively of thelevel of radiant energy on the receiver relative to said base level ofradiant energy on the receiver.
 13. A machine tool tracer according toclaim 12 wherein the spindle is elongated and is mounted on said supportfor movement of the tracing stylus in all directions through its saidestablished intermediate position, wherein the tracer comprises a pairof said photoelectric units angularly spaced substantially 90* about thelongitudinal axis of the spindle in its established intermediateposition, and wherein the shiftable masks of the pair of photoelectricunits are provided by a single masking member connected to be shifted bythe spindle in a plane substantially perpendicular to the longitudinalaxis of the spindle in its said intermediate position for variablymasking the radiant energy transmitters of the photoelectric units inaccordance with the displacement vectors of the tracing stylus alongmutually perpendicular axes respectively.
 14. A machine tool traceraccording to claim 13 wherein the spindle is mounted for rotation aboutits longitudinal axis, and wherein the tracer comprises drive means forrotating the spindle about its longitudinal axis without effecting thedisplacement of the tracing stylus from its established intermediateposition, and connector means interconnecting the spindle and maskingmember for shifting the masking member in accordance with thedisplacement of the tracing stylus from its established intermediateposition.
 15. A machine tool tracer cooperable with a workpiece templatefor controlling a workpiece machining operation comprising a support, atracing spindle mounted on the support for displacement in oppositedirections through an established intermediate position thereof andhaving a tracing stylus cooperable with a workpiece template fordisplacement in opposite directions through an established intermediateposition thereof corresponding to the established intermediate positionof the spindle, a photoelectric unit having a radiant energytransmitter, a photoelectric receiver in alignment with the transmitterfor receiving radiant energy therefrom for producing a machine toolcontrol signal, a shiftable mask mounted intermediate the radiant energytransmitter and receiver for being shifted for varying the intensity ofradiant energy on the receiver and connected to the spindle to beshifted in opposite directions as the tracing stylus is displaced inopposite directions respectively through its established intermediateposition, a stationary mask intermediate the transmitter and receiverfor masking a first peripheral portion of the transmitter, the shiftablemask being positioned, with the stylus in its said establishedintermediate position, for masking a second significant portion of thetransmitter and with a third significant portion of the transmitterunmasked, and the shiftable and stationary masks being relativelypositioned and contoured so that the shiftable mask is shifted by thespindle toward and away from the stationary mask for varying theintensity of radiAnt energy on the receiver, the spindle being elongatedand being mounted on said support for movement of the tracing stylus inall directions through its said established intermediate position, apair of said photoelectric units angularly spaced substantially 90*about the longitudinal axis of the spindle in its establishedintermediate position, and the shiftable masks of the pair ofphotoelectric units being provided by a single masking member connectedto be shifted by the spindle in a plane substantially perpendicular tothe longitudinal axis of the spindle in its said intermediate positionfor variably masking the radiant energy transmitters of thephotoelectric units in accordance with the displacement vectors of thetracing stylus along mutually perpendicular axes respectively, thespindle being mounted for rotation about its longitudinal axis, drivemeans for rotating the spindle about its longitudinal axis withouteffecting the displacement of the tracing stylus from its establishedintermediate position, connector means interconnecting the spindle andmasking member for shifting the masking member in accordance with thedisplacement of the tracing stylus from its established intermediateposition, the drive means comprising a pivotal drive sleeve surroundingthe spindle and pivotal about an axis extending transversely of thelongitudinal axis of the spindle in its established intermediateposition, the drive sleeve having a pair of diametrically opposed slots,and a pair of guide rollers received within said slots and mounted onthe spindle for rotation about an axis extending generally parallel tothe pivotal axis of the drive sleeve.
 16. A machine tool tracercooperable with a workpiece template for controlling a workpiecemachining operation comprising a support, a tracing spindle mounted onthe support for displacement in opposite directions through anestablished intermediate position thereof and having a tracing styluscooperable with a workpiece template for displacement in oppositedirections through an established intermedaite position thereofcorresponding to the established intermediate position of the spindle, aphotoelectric unit having a radiant energy transmitter, a photoelectricreceiver in alignment with the transmitter for receiving radiant energytherefrom for producing a machine tool control signal, a shiftable maskmounted intermediate the radiant energy transmitter and receiver forbeing shifted for varying the intensity of radiant energy on thereceiver and connected to the spindle to be shifted in oppositedirections as the tracing stylus is displaced in opposite directionsrespectively through its established intermediate position, a stationarymask intermediate the transmitter and receiver for masking a firstperipheral portion of the transmitter, the shiftable mask beingpositioned, with the stylus in its said established intermediateposition, for masking a second significant portion of the transmitterand with a third significant portion of the transmitter unmasked, andthe shiftable and stationary masks being relatively positioned andcontoured so that the shiftable mask is shifted by the spindle towardand away from the stationary mask for varying the intensity of radiantenergy on the receiver, the spindle being elongated and being mounted tobe displaced in opposite directions generally parallel to itslongitudinal axis, the shiftable mask being pivotally mounted andconnected for being pivotally shifted by the spindle, and the spindlebeing mounted for pivotal displacement as well as longitudinaldisplacement and means interconnecting the pivotal mask and spindle forpivoting the mask by pivotal displacement of the spindle.
 17. A machinetool tracer according to claim 16 wherein the interconnecting meanscomprises a pair of opposed ball seats on the mask and at one end of thespindle and a ball bearing received in said opposed seats.
 18. A machinetool tracer cooperable with a workpiece template for contRolling aworkpiece machining operation comprising a support, a tracing spindlemounted on the support for displacement in opposite directions throughan established intermediate position thereof and having a tracing styluscooperable with a workpiece template for displacement in oppositedirections through an established intermediate position thereofcorresponding to the established intermediate position of the spindle, aphotoelectric unit having a radiant energy transmitter, a photoelectricreceiver in alignment with the transmitter for receiving radiant energytherefrom for producing a machine tool control signal, a shiftable maskmounted intermediate the radiant energy transmitter and receiver forbeing shifted for varying the intensity of radiant energy on thereceiver and connected to the spindle to be shifted in oppositedirections as the tracing stylus is displaced in opposite directionsrespectively through its established intermediate position, a stationarymask intermediate the transmitter and receiver for masking a firstperipheral portion of the transmitter, the shiftable mask beingpositioned, with the stylus in its said established intermediateposition, for masking a second significant portion of the transmitterand with a third significant portion of the transmitter unmasked, andthe shiftable and stationary masks being relatively positioned andcontoured so that the shiftable mask is shifted by the spindle towardand away from the stationary mask for varying the intensity of radiantenergy on the receiver, the spindle being elongated and being mounted onsaid support for movement of the tracing stylus in all directionsthrough its said established intermediate position, a pair of saidphotoelectric units angularly spaced substantially 90* about thelongitudinal axis of the spindle in its established intermediateposition, the shiftable masks of the pair of photoelectric units beingprovided by a single masking member connected to be shifted by thespindle in a plane substantially perpendicular to the longitudinal axisof the spindle in its said intermediate position for variably maskingthe radiant energy transmitters of the photoelectric units in accordancewith the displacement vectors of the tracing stylus along mutuallyperpendicular axes respectively, a ball and socket support for thespindle for mounting the spindle for pivotal movement in all directionsfrom its established intermediate position and contoured tolongitudinally shifted the spindle upon pivotal displacement thereof,and a control switch connected to be actuated by the spindle upon apredetermined longitudinal displacement thereof.
 19. A machine tooltracer cooperable with a workpiece template for controlling a workpiecemachining operation comprising a support, a tracing spindle mounted onthe support for displacement in opposite directions through anestablished intermediate position thereof and having a tracing styluscooperable with a workpiece template for displacement in oppositedirections through an established intermediate position thereofcorresponding to the established intermediate position of the spindle, aphotoelectric unit having a radiant energy transmitter, a photoelectricreceiver in alignment with the transmitter for receiving radiant energytherefrom for producing a machine tool control signal, a shiftable maskmounted intermediate the radiant energy transmitter and receiver forbeing shifted for varying the intensity of radiant energy on thereceiver and connected to the spindle to be shifted in oppositedirections as the tracing stylus is displaced in opposite directionsrespectively through its established intermediate position, a stationarymask intermediate the transmitter and receiver for masking a firstperipheral portion of the transmitter, the shiftable mask beingpositioned, with the stylus in its said established intermediateposition, for masking a second significant portion of the transmitterand with a third significant portion of the transmittEr unmasked, andthe shiftable and stationery masks being relatively positioned andcontoured so that the shiftable mask is shifted by the spindle towardand away from the stationary mask for varying the intensity of radiantenergy on the receiver, the spindle being elongated and being mounted tobe displaced in opposite directions generally parallel to itslongitudinal axis and the shiftable mask being pivotally mounted forpivotal movement about an axis extending substantially perpendicular toand laterally offset from the longitudinal axis of the spindle and beingconnected for being pivotally shifted by the spindle, and spring meansinterconnecting the spindle and pivotal mask for biasing the mask in onepivotal direction for increasingly masking the transmitter and biasingthe spindle in a longitudinal direction toward the mask.